Some types of semiconductor devices are fabricated by techniques wherein doping of semiconductor material with donor and acceptor impurities is achieved by vaporizing and then recondensing a molten mixture of semiconductor material and impurities to grow crystals having the desired material characteristics. Other types are produced by alloying techniques wherein a particle of the impurities alloy is placed upon the surface of a substrate of semiconductor material and the two are heated to a temperature sufficient to cause the alloy to melt and dissolve away the adjacent semiconductor surface. The molten semiconductor alloy component is then cooled and recrystallized leaving a layer of highly doped semiconductor material and a junction of layers with the original piece of semiconductor material. The conventional diffusion process for producing semiconductor devices with junctions of two materials also requires heat.
Each of the crystal-growth, alloy and diffusion processes require that the semiconductor material be heated to a relatively high temperature, often in the order of 1,100.degree.C to 1,200.degree.C, to produce the required junction. This use of heat degrades the mean life of the minority charge carriers in the processed semiconductor material. In the case where silicon is used as the semiconductor material, devices with minority charge carrier lifetimes of as little as approximately one microsecond or less have been produced. While low lifetimes are tolerable in many transistors, other applications of semiconductor devices require long lifetime. These include, for example, solar cells, photoconductive cells and microwave semiconductor devices.
The problem of lifetime degradation due to the processes used in semiconductor junction formation has been overcome, to some extent, in processes which employ high-energy accelerators, e.g., the ion implant method, and do not require high temperatures. The considerable expense associated with these processes, however, limits their utility.